Inspection method and inspection apparatus using electron beam

ABSTRACT

An inspection method and an inspection apparatus using an electron beam enabling more detailed and quantitative evaluation at a high throughput level. The method comprises the steps of irradiating, based on previously prepared information concerning a defect position on the surface of a sample, the defect and its vicinity with an electron beam a plurality of times at predetermined intervals; detecting an electron signal secondarily generated from the sample surface by the electron beam; imaging an electron signal detected by the previously specified n-th or later electron beam irradiation; and measuring the resistance or a leakage amount of the defective portion of the sample surface in accordance with the degree of charge relaxation by monitoring the charge relaxation state of the sample surface based on the electron beam image information.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an inspection method and aninspection apparatus using an electron beam, both of which inspect asample such as a semiconductor device having micro-fabricated patterns,a substrate, a photomask (a mask having patterns formed thereon, whichis used for exposing patterns on a substrate), and a liquid crystalplate.

[0003] 2. Description of the Related Art

[0004] Semiconductor devices such as memories and microcomputers usedfor computers, etc. are manufactured through the repetition oftranscription processes such as exposing, lithographing, or etchingpatterns such as circuits, which are formed on photomasks. In themanufacturing process of semiconductor devices, the manufacturing yieldis greatly affected by several factors. These include whether or not theresults of the lithography process, etching process, or other processesinvolved are satisfactory. Yield is also affected by the presence orabsence of foreign matter of the like. Therefore, in order to detectearly or in advance the occurrence of abnormalities or defects, patternson a semiconductor wafer are inspected at the end of each manufacturingprocess.

[0005] As one example of a method for inspecting defects present in apattern on a semiconductor wafer, an optical visual inspection apparatushas been put into practice, wherein the comparison of patterns isperformed using optical images obtained through light irradiation of asemiconductor wafer. However, as circuits have miniaturized (micro)patterns and complicated shapes, and as materials used for circuits havebecome diversified, it is difficult to detect these defects usingoptical images. Thus, a method and an apparatus for inspecting a patternusing an electron beam image that has higher resolution than an opticalimage have been put into practice.

[0006] Known are technologies disclosed, for example, in JP PatentPublication (Kokai) No. 59-192943, JP Patent Publication (Kokai) No.5-258703, Sandland, et al., “An electron-beam inspection system forx-ray mask production,” J. Vac. Sci. Tech. B, Vol. 9, No. 6, pp.3005-3009 (1991), Meisburger, et al., “Requirements and performance ofan electron-beam column designed for x-ray mask inspection,” J. Vac.Sci. Tech. B, Vol. 9, No. 6, pp. 3010-3014 (1991), Meisburger, et al.,“Low-voltage electron-optical system for the high-speed inspection ofintegrated circuits,” J. Vac. Sci. Tech. B, Vol. 10, No. 6, pp.2804-2808 (1992), Hendricks, et al., “Characterization of a NewAutomated Electron-Beam Wafer Inspection System,” and SPIE Vol. 2439,pp. 174-183 (Feb. 20-22, 1995).

[0007] In order to achieve high throughput and highly accurateinspections in line with the increase of wafer bore diameter and theminiaturization of circuit patterns, there is a need to obtain a high SNimage at very high speeds. To this end, the number of electrons emittedthrough the use of a larger beam, with a current 1,000 times or more(100 nA or more) greater than that of an ordinary scanning electronmicroscope (hereinafter referred to as an SEM), should be preserved toensure the maintenance of a high SN ratio. Further, it is essential todetect secondary electrons generated from a substrate and reflectedelectrons at high speeds and with high efficiency.

[0008] Furthermore, in order to prevent a semiconductor substrate with ainsulating film such as a resist from being affected by charging, it isnecessary to apply a low accelerated electron beam of 2 keV or less.This technology is disclosed in the “Electron/Ion beam handbook (2ndedition),” edited by the 132nd Committee of Japan Society for thePromotion of Science, pp. 622-623, Nikkan Kogyo Shimbun (1986). However,the use of the low accelerated electron beam with a large currentgenerates aberrations due to the space charge effect, and therebyhigh-resolution observation has been difficult.

[0009] As a method for solving this problem, a technology wherein ahighly accelerated electron beam is decelerated directly before a sampleand is applied to the sample substantially as a low-speed acceleratedelectron beam is known. Such technology is disclosed in, for example, JPPatent Publication (Kokai) No. 2-142045 and JP Patent Publication(Kokai) No. 6-139985.

[0010] With respect to an inspection apparatus using the above SEM, thefollowing problems have yet to be solved.

[0011] One problem is that detailed evaluation is impossible because thepresence of defects is digitally judged as being 0 or 1, and during thisperiod analog judgment cannot be performed. Taking a non-opening defectof a plug hole bottom as an example, this means that it isconventionally judged to be conductive or non-conductive, but incontrast there also exists an intermediate, semi-conductive state.However, a plug is originally required to permit low resistance andohmic connections among levels of wirings. In view of this point, it canbe said that a detailed analog evaluation should be conducted using theresistance.

[0012] Further, refresh defects of DRAMs, transistor leakage defects offlash memories, or the like, though they are categorized as the sametype of electric characteristic defects, are caused by a micro leakagecurrent of a pn junction, and these defects are difficult to detect evenwith an SEM inspection apparatus. JP Patent Publication (Kokai) No.2002-9121 discloses attempts to detect the above defects byintermittently applying an electron beam in a condition where a junctionis charged in a reverse biased state, and detecting the defect as anelectric potential contrast image using a state where the charge isrelaxed through a junction leakage current.

[0013] However, in this method, since the irradiation of the electronbeam at the same location is repeated many times, it is necessary tomove a wafer in a step-and-repeat manner. Therefore, when stationarytime of a stage mechanism or time lost through stage control is takeninto consideration, a problem arises, in which the throughput, evaluatedin terms of the time required for one semiconductor substrate,deteriorates.

SUMMARY OF THE INVENTION

[0014] The present invention has been accomplished in view of the abovepoints, and thus has an object of providing an inspection method and aninspection apparatus using an electron beam, which enables a highthroughput of more detailed and quantitative evaluation, by using an SEMinspection apparatus as technology for inspecting characteristicelectric defects that are difficult to detect through optical images andby making it possible not only to judge conductiveness ornon-conductiveness, etc., but also to measure the resistance or aleakage current amount at a pn junction.

[0015] An embodiment of the present invention is an inspection apparatususing an electron microscope for detecting a defect on a pattern of asample based on a detection signal of secondary charged particlesgenerated by scanning an electron beam, wherein a rough inspection fornarrowing down defect candidates is first conducted and defect review isperformed, and then the resistance or leakage amount of a defectiveportion is measured.

[0016] More specifically, a method of the present invention comprisesthe steps of: irradiating, based on previously prepared informationconcerning a defect position on the surface of a sample, the defect andits vicinity with an electron beam a plurality of times at predeterminedintervals; detecting an electron signal secondarily generated from thesample surface by the electron beam; imaging the electron signaldetected by the previously specified n-th or later electron beamirradiation; and measuring the resistance or a leakage amount of adefective portion of the sample surface in accordance with the degree ofcharge relaxation by monitoring a charge relaxation state of the samplesurface based on information of the electron beam image.

[0017] This specification includes part or all of the contents asdisclosed in the specification and/or drawings of Japanese PatentApplication No. 2002-180735, which is a priority document of the presentapplication.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a vertical cross sectional view showing a configurationof a SEM type visual inspection apparatus.

[0019]FIG. 2 is a function block diagram of an embodiment of the presentinvention.

[0020]FIG. 3 is a flow chart showing an inspection procedure.

[0021]FIG. 4 is a flow chart showing an inspection procedure.

[0022]FIG. 5 is a relationship diagram illustrating a principle formeasuring the resistance of a defective portion.

[0023]FIG. 6 is a plan view of a wafer holder.

[0024]FIG. 7 is a screen view showing an example display on a monitor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Preferred embodiments of the present invention will hereinafterbe described with reference to the accompanying drawings.

[0026]FIG. 1 is a vertical cross sectional view illustrating aconfiguration of an SEM type visual inspection apparatus 1 as oneexample of an inspection apparatus using a scanning electron microscopeto which the present invention is applied. The SEM type visualinspection apparatus 1 comprises an inspection chamber 2, the inside ofwhich is evacuated, and a spare chamber (not shown in the presentembodiment) for conveying a sample substrate 9 into the inspectionchamber 2. These inspection chamber 2 and spare chamber are configuredso that they are independently evacuated. In addition to the aboveinspection chamber 2 and spare chamber, the SEM type visual inspectionapparatus 1 is composed of an image processing unit 5, a controller 6,and a secondary electrons detection unit 7.

[0027] The inside of the inspection chamber 2 is roughly divided into anelectron optics system 3, a sample chamber 8, and an optical microscopeunit 4. The electron optics system 3 comprises an electron gun 10, anelectron-beam drawing electrode 11, a condenser lens 12, a blankingdeflector 13, a scan deflector 15, a diaphragm 14, an objective lens 16,a reflecting plate 17, and an ExB deflector 18. A secondary electrondetector 20 of the secondary electrons detection unit 7 is disposedabove the objective lens 16 in the inspection chamber 2. An outputsignal of the secondary electron detector 20 is amplified by apreamplifier 21 provided outside the inspection chamber 2, which in turnis converted into digital data by an AD converter 22.

[0028] The sample chamber 8 comprises a sample table 30, an X stage 31,a Y stage 32, a position monitoring length-measuring device 34, and asample substrate height measuring device 35. The optical microscope unit4 is located in the vicinity of the electron optics system 3 lyingwithin the inspection chamber 2 and is installed at a position wherethey are distant from each other to such an extent that they do notexert influence on each other. The distance between the electron opticssystem 3 and optical microscope unit 4 is known. Further, the X stage 31or the Y stage 32 moves forward and backward alternately between theelectron optics system 3 and the optical microscope unit 4. The opticalmicroscope unit 4 comprises a light source 40, an optical lens 41, and aCCD camera 42.

[0029] The image processing unit 5 comprises a first image storage part46, a second image storage part 47, an operation part 48, and a defectdetermination part 49. A captured electron-beam image or optical imageis displayed on a monitor 50.

[0030] Operation instructions and operating conditions used for therespective parts of the apparatus are inputted to and outputted from thecontroller 6. Conditions such as accelerating voltage, deflected widthand a deflection speed of an electron beam at the occurrence of theelectron beam, timings for capturing signals by the secondary electronsdetection unit 7, a sample table traveling speed, and others have beeninputted in advance to the controller 6 so that they can be arbitrarilyor selectively set depending on purposes. The controller 6 monitorsshifts or displacements in position and height from signals outputtedfrom the position monitoring length measuring device 34 and the samplesubstrate height measuring device 35 by the use of the correctioncontrol circuit 43. Based on the results of the monitoring, thecontroller 6 enables the correction control circuit 43 to generate acorrection signal, and to send the correction signal to the objectivelens source 45 and a scan signal generator 44, so that an electron beamis always applied to the proper position.

[0031] In order to obtain an image of the sample substrate 9, athinly-focused electron beam 19 is applied to the sample substrate 9 tothereby produce secondary electrons 51. They are detected in synchronywith the scanning of the electron beam 19 and the movements of the Xstage 31 and the Y stage 32, thereby obtaining the image of the samplesubstrate 9.

[0032] It is essential to enhance the inspection speed for the SEM typevisual inspection apparatus. Therefore, unlike an ordinary conventionaltype of SEM, the SEM type visual inspection apparatus does not performthe scanning of an electron beam of an electron-beam current on theorder of pA at low speeds, perform the scanning a large number of times,or perform the superimposition of respective images on one another.Further, for the purpose of restricting charging on an insulatingmaterial, it is necessary to scan the electron beam once or severaltimes at high speed, rather than many times. Thus, in the presentembodiment, an electron beam having a larger current of, for example,100 nA, which is about 1,000 times or more greater than that of aconventional SEM, is scanned once alone to thereby form an image.

[0033] A diffusion refill-type thermofield emission electron source isused for an electron gun 10. The use of this electron gun 10 makes itpossible to ensure an electron beam current remains stable as comparedwith, for example, a tungsten filament electron source and a cold fieldemission type electron source. Therefore, an electron beam image thatshows little change in brightness can be obtained. Further, since theelectron gun 10 enables the electron beam current to be set at a highlevel, the high-speed inspection described below can be realized. Theelectron beam 19 is drawn from the electron gun 10 by applying a voltagebetween the electron gun 10 and the drawing electrode 11.

[0034] The electron beam 19 is accelerated by applying a negativepotential with a high voltage to the electron gun 10. This enables theelectron beam 19 to move to the sample table 30 by means of energyequivalent to the potential, followed by convergence on the condenserlens 12. Further, the electron beam 19 is thinly-focused by theobjective lens 16 to be applied to the sample substrate 9 mounted on theX stage 31 and the Y stage 32 placed on the sample table 30. The samplesubstrate 9 is a semiconductor wafer, a chip, or a substrate having amicro-fabricated circuit pattern such as a liquid crystal, a mask, orthe like. The scan signal generator 44 for generating a scan signal anda blanking signal is connected to the blanking deflector 13, and theobjective lens source 45 is connected to the objective lens 16.

[0035] To the sample substrate 9, negative voltage can be applied by ahigh-voltage power supply 36. By adjusting the voltage of thishigh-voltage power supply 36, the electron beam 19 is decelerated andelectron beam irradiation energy applied to the sample substrate 9 canbe adjusted to an optimum value without changing the potential of theelectron gun 10.

[0036] The secondary electrons 51 generated by applying the electronbeam 19 to the sample substrate 9 are accelerated under the negativevoltage applied to the sample substrate 9. The ExB deflector 18 isdisposed above the sample substrate 9. The deflector 18 is used forturning the orbit of secondary electrons by means of both electric andmagnetic fields without affecting the orbit of the electron beam 19.This enables the accelerated secondary electrons 51 to be deflected in apredetermined direction. The intensities of the electric and magneticfields applied to the ExB deflector 18 allow adjustments to the amountof deflection of secondary electrons. In addition, these electric andmagnetic fields can be varied in conjunction with the negative voltageapplied to the sample substrate 9.

[0037] The secondary electrons 51 deflected by ExB deflector 18 collidewith the reflecting plate 17 under predetermined conditions. Thereflecting plate 17 has a conical shape and also has a function as ashield pipe to shield the electron beam 19 applied to the samplesubstrate 9. When the accelerated secondary electrons 51 collide withthis reflecting plate 17, second secondary electrons 52, having energyfrom a few eV to 50 eV, are produced from the reflecting plate 17.

[0038] The secondary electrons detection unit 7 has the secondaryelectron detector 20 provided within the evacuated inspection chamber 2.A preamplifier 21, an AD converter 22, an optical converting means 23,optical transmission means 24, an electric converting means 25, ahigh-voltage power supply 26, a preamplifier drive source 27, an ADconverter drive source 28, and a reverse bias source 29 are providedoutside the inspection chamber 2, which constitutes the secondaryelectrons detection unit 7.

[0039] The secondary electrons detector 20 of the secondary electronsdetection unit 7 is placed above the objective lens 16 inside theinspection chamber 2. The secondary electrons detector 20, preamplifier21, AD converter 22, optical converting means 23, preamplifier drivepower source 27, and AD converter drive power source 28 are renderedfloating at a positive potential by the high-voltage power supply 26.The second secondary electrons 52 generated from the collision of thesecondary electrons 51 with the reflecting plate 17 are introduced intothe secondary electrons detector 20 under the action of a drawingelectric field created by the positive potential.

[0040] The secondary electrons detector 20 is configured so as to detectthe second secondary electrons 52 generated by the collision of thesecondary electrons 51 with the reflecting plate 17 in conjunction withthe time when the electron beam 19 is scanned. An output signal of thesecondary electrons detector 20 is amplified by the preamplifier 21provided outside the inspection chamber 2, which in turn is convertedinto digital data by the AD converter 22.

[0041] The AD converter 22 is configured so as to convert an analogsignal detected by the secondary electrons detector 20 into a digitalsignal immediately after the preamplifier 21 amplifies the signal, andthen transmit the signal to the image processing unit 5. Since thedetected analog signal is digitized and transmitted immediately afterits detection, a signal having a higher speed and S/N ratio than aconventional signal can be obtained.

[0042] The sample substrate 9 is mounted on the X stage 31 and the Ystage 32. Either one of a method for stopping the X stage 31 and the Ystage 32 upon the execution of an inspection to therebytwo-dimensionally scan the electron beam 19, and a method forsequentially moving the X stage 31 and the Y stage 32 in a Y directionat a constant speed upon the execution of the inspection to therebylinearly scan the electron beam 19 in an X direction can be selected. Inthe case of inspecting a relatively small specific given area, theformer method of stopping the sample substrate 9 for inspection iseffective. In the case of inspecting a relatively wide area, the methodof consecutively moving the sample substrate 9 at a constant speed forinspection is effective. In addition, when blanking on the electron beam19 is necessary, the electron beam 19 is deflected by the blankingdeflector 13 so that the electron beam is controlled so as not to passthrough the diaphragm 14.

[0043] In the present embodiment, a laser interference-based wavemeteris used as the position monitoring length-measuring device 34 formonitoring the positions of the X stage 31 and the Y stage 32. Thepositions of the X stage 31 and the Y stage 32 can be monitored in realtime, and the results thereof are to be transferred to the controller 6.Further, the present embodiment is configured so that data itemsconcerning the numbers of revolutions of motors used for the X stage 31,Y stage 32, etc. are also transferred from their drivers to thecontroller 6 in the same manner. The controller 6 is able to accuratelygrasp each area and position irradiated with the electron beam 19 basedon these data items. Therefore, when a position irradiated with theelectron beam 19 is deviated from an intended position, the correctioncontrol circuit 43 can correct the position in real time, if necessary.Further, areas irradiated with the electron beam 19 can be stored forevery sample substrate 9.

[0044] The sample substrate height measuring device 35 utilizes anoptical measuring instrument, e.g., a laser interference measuringinstrument or a reflected-light type measuring instrument for measuringthe position change of reflected light. It is configured so as tomeasure the height of the sample substrate 9 mounted on the X stage 31and the Y stage 32 in real time. The present embodiment employs a methodcomprising the steps of applying a slender white light transmittedthrough a slit to the sample substrate 9 through a transparent window,detecting the position of the reflected light thereof by a positiondetecting monitor, and calculating the amount of height change from thevariation in position. Based on data measured by this optical heightmeasuring device 35, the focal distance of the objective lens 16 isdynamically corrected, whereby the electron beam 19 that is focused oneach area to be inspected can be always applied. Further, warpage orheight distortion of the sample substrate 9 is measured in advancebefore the application of the electron beam, and based on the datathereof, the objective lens 16 may also be configured so that correctionconditions thereof are set for each inspected area.

[0045] The image processing unit 5 comprises a first image storage part46, a second image storage part 47, an operation part 48, a defectdetermination part 49 and a monitor 50. An image signal on the samplesubstrate 9 detected by the secondary electrons detector 20 is amplifiedby the preamplifier 21 and digitized by the AD converter 22. Thereafterit is converted into a light signal by an optical converting means 23and transmitted by an optical transmitting means 24. Then, it isconverted again into an electric signal by an electric converting means25, and the thus obtained signal is stored in the first or second imagestorage part 46 or 47. The operation part 48 performs an alignmentbetween the image signal stored in the first image storage part 46 andthe image signal stored in the second image storage part 47,standardization of signal level, and various image processes forremoving noise signals. It also computes both the image signals forcomparison. The defect determination part 49 compares the absolute valueof the differential image signal computed for comparison by theoperation part 48 with a predetermined threshold value. When the levelof the differential image signal is larger than the predeterminedthreshold value, the defect determination part 49 judges their pixels asdefect candidates, and their positions, the number of defects, etc. aredisplayed on the monitor 50.

[0046] Next, the operation of each part of the inspection apparatusshown in FIG. 1 will be described according to the inspection procedureshown in FIG. 3. FIG. 3 shows a flowchart of the inspection procedure.

[0047] First, a wafer cassette having a wafer placed on the desiredshelf is placed on a cassette placement part of a wafer transportationsystem (Step 310 of FIG. 3).

[0048] Next, in order to specify the wafer to be inspected, the numberof the cassette shelf having the wafer placed thereon is entered throughan operation screen. Then, through the operation screen variousinspection conditions are inputted (Step 320 of FIG. 3). The inspectioncondition parameters to be inputted include those involving electronbeam current, electron beam irradiation energy, scanning speed andsignal detection sampling clock, the area to be inspected, and varioustypes of information regarding the wafer to be inspected. Further, thecontent concerning whether a plurality of wafers are to be automaticallyand continuously inspected one by one, whether one wafer is to beinspected continuously under different conditions, or the like areinputted as inspection condition parameters. These parameters can beindividually inputted, but usually the combinations of the above variousinspection condition parameters are stored in a database as inspectioncondition data files. Therefore, it is necessary to select and input onefile among inspection condition data files. When the input of theseconditions is completed (Step 320 of FIG. 3), the inspection starts(Step 330 of FIG. 3).

[0049] When automatic inspection starts, a predetermined wafer is firsttransported into the inspection apparatus. When wafers to be inspectedhave different diameters, or when wafers have different shapes fallingbetween those of the orientation flat type and notch type, the wafertransportation system can deal with these cases by replacing one holderfor placing a wafer with another in accordance with the sizes or shapesof wafers. The wafer to be inspected is transported from the wafercassette onto the wafer holder by the wafer loader, which includes anarm and a preliminary vacuum chamber. The wafer is securely held andsubjected to evacuation together with the holder inside the waferloader, and then transported to the inspection chamber that has alreadybeen evacuated by the evacuation system (Step 340 of FIG. 3). When thewafer is loaded, electron beam irradiation conditions for each part areset by an electron optics system controller based on the above inputtedinspection condition parameters.

[0050]FIG. 6 is a plane view of a wafer holder 750 on which a wafer 760is placed. The wafer holder 750 as shown in FIG. 6 has a beamcalibration pattern 770 placed thereon. A stage moves so that the beamcalibration pattern comes beneath the electron optics system (Step 350of FIG. 3), and an electron beam image of the beam calibration pattern770 is obtained for making focal and astigmatic adjustments according tothe obtained image. Then, the stage moves further so that the electronoptics system is located above a specific point of the wafer to beinspected to obtain an electron beam image of the wafer and to adjust acontrast image or the like. At this time, when it is necessary to modifythe electron beam irradiation conditions, etc., the parameters aremodified and the beam calibration can be performed again. At the sametime the height of the wafer is obtained by the height detector, a waferheight detection system computes the correlation between the heightinformation and electron beam focusing conditions. Thereafter, wheneveran electron beam image is obtained, an automatic adjustment of thefocusing conditions is made based on the results of the wafer heightdetection, without the need for focusing each time. This enableselectron beam images to be obtained continuously and at high speeds(Step 360 of FIG. 3).

[0051] When the input of the electron beam irradiation conditions andthe focal/astigmatic adjustment are completed, alignment is performed inaccordance with two points on the wafer (Step 370 of FIG. 3).

[0052] After the alignment is completed, the rotation or coordinatevalues are corrected based on the results of the alignment. Then, thestage moves so that the electron optics system is located above a secondcalibration pattern 780 placed on the wafer holder 750 as shown in FIG.6 (Step 380 of FIG. 3). The second calibration pattern 780 is atransistor or a pattern corresponding to a transistor having a normaljunction formed thereon in advance. Using that pattern, the brightnessof a normal portion is calibrated. Based on the results of thecalibration, the electron optics system is located above the wafer toobtain an image of a pattern point on the wafer and perform brightnessadjustment: in other words, calibration (Step 390 of FIG. 3).

[0053] After the calibration is completed, the inspection is performed(Step 400 of FIG. 3). With respect to the inspection method, while thestage is continuously moved to conduct the inspection of specifiedareas, the image processing is carried out on a real-time basis and animage of a defect occurrence point is automatically stored (Step 410 ofFIG. 3). Then, the inspection result is displayed on the monitor 50, andthe data is outputted to the outside through a data conversion part(Step 420 of FIG. 3).

[0054] For inputting the inspection conditions (Step 320 of FIG. 3),when the condition is set wherein one point is inspected several timesunder different conditions, a charge elimination process is carried outon the area that has been once inspected (Step 440 of FIG. 3). Althougha charge-elimination part is not shown in FIG. 1, the charge eliminationprocess is carried out, for example, by the application of ultravioletlight.

[0055] Then, an inspection is carried out again under different electronbeam irradiation conditions (Step 400 of FIG. 3). In this way, when theinspection is completed, the wafer is unloaded and the inspection isfinished (Step 430 of FIG. 3).

[0056]FIG. 2 is a function block diagram showing an embodiment of thepresent invention. The inspection performed in accordance with theinspection procedure described above is regarded as a rough inspection.Based on the results of this rough inspection, defect candidates arenarrowed down. Thereafter, detailed inspection as shown below is carriedout.

[0057] Namely, the inspections performed and the output of resultsobtained at Steps 400, 410, and 420 of FIG. 3 are represented as defectinformation 220 outputted from the image processing unit 5 in FIGS. 2(a) and (b). Based on this defect information 220, defect positioninformation 240 is generated by a defect position information generatingunit 230. The stage is moved so as to bring a defect position indicatedby the defect position information 240 underneath the electron opticssystem, and a resistance/leakage amount measuring unit 250 measures theresistance and a leakage amount 260 (detailed inspection).

[0058] Since the rough inspection of the entire wafer is conducted athigh speed by continuously moving the stage to narrow down defectcandidates, and then a detailed inspection is conducted, which takesmore time, the entire inspection efficiency can be greatly improved.

[0059] In FIG. 2(b), the stage is moved based on the defect positioninformation 240, and a defect is reviewed by a defect review processingunit 270. Thereafter, the resistance and leakage amount are measured.While doing this, defect candidates are further narrowed down by defectreview, and the inspection efficiency can be further enhanced.

[0060]FIG. 4 is a flow chart showing an inspection procedure. Withreference to FIG. 4, the inspection procedure shown in FIG. 2(b) isdescribed in detail.

[0061] First, a wafer cassette having a wafer placed on a desired shelfis placed on a cassette placement part of a wafer transportation system(Step 510 of FIG. 4).

[0062] Next, in order to specify a wafer to be inspected, the number ofthe cassette shelf having the wafer placed thereon is entered through anoperation screen. Then, through the operation screen the results of arough inspection previously conducted are inputted (Step 520 of FIG. 4).The input contents include file names storing the inspection results.

[0063] When the input is completed, a defect review starts (Step 530).Once automatic defect review starts, first the predetermined wafer istransported into the inspection apparatus and then transported to aninspection chamber that has been already evacuated by the evacuationsystem (Step 540 of FIG. 4).

[0064] When the wafer is loaded, the stage is moved so as to bring adefect position underneath the electron optics system based on thedefect position information as the above inputted results of the roughinspection (Step 550). The defect is displayed on the monitor 50 forreviewing (Step 560).

[0065] Thereafter, the process is shifted to a resistance measurementmode (Step 600).

[0066] Next, the electron beam irradiation condition is tentatively setat Step 610. Since the principle disclosed in JP Patent Publication(Kokai) No. 2002-9121 described above is used for measurement, anelectron beam current amount, an XY scanning size, an irradiationinterval, the number of irradiation times, etc. are tentatively set. AtStep 620, an image corresponding to these conditions is displayed, andit is judged whether these conditions are suitable for measurement atStep 630. If the conditions are not suitable, the process returns toStep 610 to adjust the conditions. After suitable conditions aredetermined, the resistance of the defective portion is measured at Step640.

[0067] Thereafter, the resistance measurement mode is finished, and theresults of review, the results of resistance measurement, or the likeare outputted at Step 570. With respect to subsequent defects, the sameprocesses are repeated. Then, after the processes for all the defectsare finished, the wafer is unloaded at Step 590 and then the process isfinished.

[0068]FIG. 5 is a relationship diagram illustrating a principle formeasuring the resistance of a defective portion. The horizontal axisrepresents time, and the vertical axis represents the amount of electronbeam irradiation and charged voltage, or SEM image brightness. Thedetailed principle of a method for resistance measurement of a defectiveportion is disclosed in JP Patent Publication (Kokai) No. 2002-9121.FIG. 5 shows an example plug having a shorter charge relaxation timethan a plug having a pn junction with a normal electron beam irradiationinterval T_(int). In this case, after electron beam is applied aplurality of times, a difference between the normal plug 700 and leakagedefect plug 710 in SEM image brightness occurs as shown in the figure.When the difference is classified quantitatively, the degree of leakage,namely the resistance component, can be estimated. For example, when thedifference is larger, the resistance is estimated to be smaller.

[0069]FIG. 6 is a plane view of a wafer holder as mentioned above.Several types of leakage samples generated from a normal pn junction areprepared in the second calibration pattern 780 provided on the waferholder 750, and these are compared with the SEM image brightness of eachdefective portion. This enables more accurate quantitative evaluation.By doing this, the estimation of absolute resistance can be achieved.

[0070]FIG. 7 is a screen view showing an example display on a monitor.The example display of FIG. 7 includes the measurement resultsconcerning the resistance of defects. On left side of a screen 800, awafer map 810 is displayed, and defects are indicated on the map bycircular signs. Portions where leakage defects occur are indicated as adistribution pattern. In an area 820, legends for the distributionpattern of leakage defective portions as shown in the wafer map 810 aredisplayed, and in this example, the resistance is classified into threetypes. Each type may be distinguished by color to easily and visuallyidentify them. In the figure, “XX” and “YY” practically representspecific values of the resistance. These values can be arbitrarily set.Further, the conditions at the time of measuring the resistance in thisexample are displayed in an area 830. An electron beam current amount, ascanning size in each direction of X or Y axis, an irradiation intervalof the electron beam, and the number of times for electron beamirradiation on the same area are displayed in an area 832, an area 834,an area 836, and an area 838, of the area 830, respectively.

[0071] Defects such as leakage defects are greatly affected by processconditions, and therefore, for example, some defects are likely to occuraround the wafer. According to this embodiment, such distributioncharacteristic can be more accurately grasped.

[0072] Although defects such as leakage defects are indicated on thedistribution on the wafer in this embodiment, they may be indicated as adistribution on each chip of the wafer. In this case, the wafer map 810as shown in FIG. 7 may display one chip or a plurality of chips.

[0073] The above embodiments according to the present invention aresummarized as follows.

[0074] A method is provided, which comprises the steps of: irradiating,based on previously prepared information concerning a defect position onthe surface of a sample, the defect and its vicinity with an electronbeam a plurality of times at predetermined intervals; detecting anelectron signal secondarily generated from the sample surface by theelectron beam; imaging an electron signal detected by the previouslyspecified n-th or later electron beam irradiation; and measuring theresistance or a leakage amount of a defective portion of the samplesurface in accordance with the degree of charge relaxation by monitoringa charge relaxation state of the sample surface based on the electronbeam image information.

[0075] The method may further comprise displaying image informationobtained by the imaging step.

[0076] Further, the previously prepared defect position information isgenerated based on defect inspection by continuously moving a samplestage having a wafer placed thereon. The electron beam irradiation step,electron signal detection step, and resistance/leakage amountmeasurement step are repeated in a state where the sample stage is movedsequentially and stopped at each defect position based on the defectposition information.

[0077] Furthermore, the resistance or leakage amount of each defectiveportion obtained in the resistance/leakage amount measurement step isdisplayed as in a map on a schematic diagram of the wafer organized bytype of defect.

[0078] Moreover, a method is provided comprising the steps of: scanningan electron beam on a wafer while continuously moving a sample tablehaving the wafer placed thereon; detecting an electron signalsecondarily generated from the wafer surface by the electron beam;imaging the electron signal; specifying a defective portion by comparingelectron beam images having the same pattern with each other; generatingdefect position information containing at least position informationamong attribution information of the defective portion; irradiating thedefect and its vicinity with the electron beam a plurality of times atpredetermined intervals based on the defect position information;detecting an electron signal secondarily generated from the wafersurface by the electron beam; imaging an electron signal detected by thepre-specified n-th or later electron beam irradiation; and measuring theresistance or a leakage amount of the defective portion on the wafersurface depending on the degree of charge relaxation by monitoring acharge relaxation state on the wafer surface in accordance with theelectron beam image information.

[0079] In addition, an inspection apparatus is provided, which comprisesa sample table for wafer placement; a stage mechanism unit forcontinuously moving the sample table; an electron source; an electronoptics system for applying and scanning an electron beam from theelectron source on the wafer; a detector for detecting an electronsignal secondarily generated from the wafer surface by the electronbeam; an image processing unit for imaging the electron signal andspecifying a defective portion by comparing electron beam images havingthe same pattern with each other; and a defect position informationgenerating unit for generating defect position information including atleast position information among attribute information of a defectiveposition. Here, the electron optics system has a function to irradiate,based on the defect position information, a defect and its vicinity withthe electron beam at predetermined intervals a plurality of times. Thedetector detects the electron signal secondarily generated from thewafer surface by the electron beam, and the image processing unit has afunction to image the electron signal detected by the pre-specified n-thor later electron beam irradiation. The apparatus further comprises aresistance/leakage amount measurement part for measuring the resistanceor a leakage amount of the defective portion on the wafer surfacedepending on the degree of charge relaxation by monitoring the chargerelaxation state of the wafer surface according to the electron beamimage information.

[0080] As described above, it is possible to obtain an inspection methodand an inspection apparatus enabling more detailed and quantitativeevaluation at a high throughput level, by using an SEM type inspectionapparatus as a technology for inspecting electric characteristic defectsthat are difficult to be detected by optical images, and making itpossible not only to judge conductiveness or non-conductiveness but alsoto measure the resistance or a leakage current amount at a pn junction.

EFFECT OF THE INVENTION

[0081] As mentioned above, the present invention provides an inspectionmethod and an inspection apparatus using an electron beam, which enablesmore detailed and quantitative evaluation at a high throughput level.

[0082] All publications, patents and patent applications cited hereinare incorporated herein by reference in their entirety.

What is claimed is:
 1. An inspection method using an electron beamcomprising the steps of: irradiating, based on previously preparedinformation concerning a defect position on the surface of a sample, thedefect and its vicinity with an electron beam a plurality of times atpredetermined intervals; detecting an electron signal secondarilygenerated from the sample surface by the electron beam; imaging theelectron signal detected by the pre-specified n-th or later electronbeam irradiation; and measuring the resistance or a leakage amount of adefective portion of the sample surface in accordance with the degree ofcharge relaxation by monitoring a charge relaxation state of the samplesurface based on the electron beam image information.
 2. The inspectionmethod according to claim 1, wherein the method comprises displayingimage information obtained by the imaging step.
 3. The inspection methodaccording to claim 1, wherein the previously prepared defect positioninformation is generated based on defect inspection by continuouslymoving a sample stage having the sample placed thereon, and the electronbeam irradiation step, electron signal detection step, andresistance/leakage amount measurement step are repeated in a state wherethe sample stage is moved sequentially and stopped at each defectposition based on the defect position information.
 4. The inspectionmethod according to claim 1, wherein the resistance or leakage amount ofeach defective portion obtained in the resistance/leakage amountmeasurement step is displayed as in a map on a schematic diagram of thesample organized by type of defect.
 5. An inspection method using anelectron beam comprising the steps of: scanning an electron beam on asample while continuously moving a sample table having the sample placedthereon; detecting an electron signal secondarily generated from thesample surface by the electron beam; imaging the electron signal;specifying a defective portion by comparing electron beam images havingthe same pattern with each other; generating defect position informationcontaining at least position information among attribution informationof the defective portion; irradiating the defect and its vicinity withthe electron beam a plurality of times at predetermined intervals basedon the defect position information; detecting an electron signalsecondarily generated from the sample surface by the electron beam;imaging an electron signal detected by pre-specified n-th or laterelectron beam irradiation; and measuring the resistance or a leakageamount of the defective portion on the sample surface depending on thedegree of charge relaxation by monitoring the charge relaxation state onthe sample surface in accordance with the electron beam imageinformation.
 6. An inspection apparatus using an electron beamcomprising: a sample table for sample placement; a stage mechanism unitfor continuously moving the sample table; an electron source; anelectron optics system for applying and scanning an electron beam fromthe electron source on the sample; a detector for detecting an electronsignal secondarily generated from the sample surface by the electronbeam; an image processing unit for imaging the electron signal andspecifying a defective portion by comparing electron beam images havingsubstantially the same pattern with each other; and a defect positioninformation generating unit for generating defect position informationincluding at least position information among attribute information ofthe defective position, wherein the electron optics system has further afunction to irradiate, based on the defect position information, adefect and its vicinity with the electron beam at predeterminedintervals a plurality of times, the detector detects the electron signalsecondarily generated from the sample surface by the electron beam, theimage processing unit has a function to image the electron signaldetected by the pre-specified n-th or later electron beam irradiation,and the inspection apparatus further comprises a resistance/leakageamount measurement part for monitoring the charge relaxation state ofthe sample surface according to the electron beam image information andmeasuring the resistance or a leakage amount of the defective portion onthe sample surface depending on the degree of charge relaxation.